Clover is a legume; what organism forms a symbiotic nitrogen-fixing relationship in root nodules?

Clover is a legume; what organism forms a symbiotic nitrogen-fixing relationship in root nodules?

• A. Rhizobium bacteria.
• B. Mycorrhizal fungi.
• C. Azotobacter species.
• D. Nitrosomonas bacteria.

Answer: (A)

Legumes like clover form a tightly organized partnership where bacteria inside root nodules convert atmospheric nitrogen into a form the plant can use. The partner responsible for this inside the nodules is Rhizobium bacteria. They infect the roots, trigger nodule formation, and inside those nodules they fix nitrogen using the enzyme nitrogenase. The plant supplies sugars to the bacteria, and in return the bacteria provide ammonia that the plant converts into amino acids and other nitrogen compounds. The nodules also contain leghemoglobin to keep oxygen levels low enough to protect the nitrogenase enzyme. Other organisms don’t fit this specific setup: mycorrhizal fungi help with water and phosphate uptake rather than fixing nitrogen in nodules; Azotobacter species fix nitrogen but do so as free-living soil bacteria, not inside root nodules; Nitrosomonas bacteria participate in converting ammonia to nitrite in soil, not in nitrogen fixation within plant nodules.

Legumes like clover form a tightly organized partnership where bacteria inside root nodules convert atmospheric nitrogen into a form the plant can use. The partner responsible for this inside the nodules is Rhizobium bacteria. They infect the roots, trigger nodule formation, and inside those nodules they fix nitrogen using the enzyme nitrogenase. The plant supplies sugars to the bacteria, and in return the bacteria provide ammonia that the plant converts into amino acids and other nitrogen compounds. The nodules also contain leghemoglobin to keep oxygen levels low enough to protect the nitrogenase enzyme.

Other organisms don’t fit this specific setup: mycorrhizal fungi help with water and phosphate uptake rather than fixing nitrogen in nodules; Azotobacter species fix nitrogen but do so as free-living soil bacteria, not inside root nodules; Nitrosomonas bacteria participate in converting ammonia to nitrite in soil, not in nitrogen fixation within plant nodules.